586 



NATURE 



{April 2 i^, 1879 



tion both at home and abroad, for take it all in all, as Mr. 

 BuUen says, "no catalogue in the world, whether in print 

 or in manuscript, is equal to that of the British Museum." 

 We hope, therefore, that the proposal of the Society will 

 speedily meet with a favourable response from Govern- 



ment, and that should it be decided to print the British 

 Museum Catalogue, some plan will be formed by which 

 proofs may be revised not only by qualified bibliographers, 

 but that the various departments of literature, science, 

 and art will be represented on the staff of revisers. 



A MIRROR BAROMETER 



TV/r L]£ON TEISSERENC DE BORT has invented 

 ^^ • an aneroid mirror barometer, which is described 

 in a recent number of La Nature. It is based on a method 

 analogous to that well-known since the researches of 

 Gauss for the reading of small rotations. M. Teisserenc 

 de Bort has sought to obtain an aneroid barometer which 

 will give precise observations at sea, especially in rough 

 weather, when it is impossible to read the mercury baro- 

 meter. The principle of this barometer is very simple. 

 The elastic tub or box B carries, as in most aneroids, a 

 metallic point, which follows its movements. In the 



ordinary aneroid the transformation of the vertical move- 

 ment into a rotating movement necessitates either a chain 

 or a curb, or a sort of fork which works in a spiral furrow 

 cut in the axis which supports the needle. These various 

 systems have the inconvenience of producing frictions ; 

 some of them are liable to dust and rust. In the mirror 

 barometer, the transformation of the movement is ob- 

 tained by the simple contact of a small palette supported 

 on the axis of the mirror and of the point spoken of above. 

 As the angle which the plane of the mirror may describe 

 does not exceed 12° on each side of the vertical, it follows 

 that the contact of the point in the palette is always 

 precise. 



Teisserenc de Bort's mirror barometer. 



As to the amplification of the movements necessary to 

 enable us to appreciate millimetres and their fractions, 

 this is obtained by reading with the aid of a small 

 reticled telescope, L, the image of a graduated scale E 

 which is reflected in the mirror M, By combining the 

 enlargement of the telescope with the distance of the 

 scale from the mirror, we succeed in giving to the appa- 

 ratus a length of less than 20 cm. by 12, which renders it 

 quite portable. It is important to remark that the ampli- 

 fication of the movements of the box, which, in ordinary 

 barometers, is obtained by means of several levers, is 

 obtained here by an optical process ; it follows that the 

 numerous frictions and the time lost in contacts are mostly 



eliminated. There remains only a single movement, that 

 of the axis which bears the mirror; in the barometer 

 figured the pivots are of steel and the cap of platinum, 

 and in order to avoid rust, the whole is nickel-plated. 



M. Teisserenc de Bort proposes to construct others, in 

 which the axis will be mounted on rubies. This garniture 

 will not sensibly increase the price of the apparatus. This 

 instrument is too new to allow us to appreciate the full 

 degree of precision which it can attain. In a trial in a 

 captive balloon by Capt. Perrier of several aneroids as 

 compared with the mirror, the latter showed a great sen- 

 sibility, and it quickly resumed its original position on 

 landing. 



BUTTERFLIES WITH DISSIMILAR SEXES 



"N^ATURALISTS have long been familiar with the 

 ■»-^ fact that the two sexes of certain species of lepi- 

 doptera often differed from each other ;in colour and 

 marking, and sometimes in form and size to a very consi- 

 derable extent. For this phenomenon the convenient 

 term "Antigeny" has been proposed by Mr. S. H. 

 Scudder.' In accordance with Darwin's theory of sexual 

 selection we find that when the sexes of a butterfly differ 

 to any marked extent in colour, it is generally the male 

 which is the more gaudily coloured, although there are 

 certain genera in which the reverse obtains ; but, as I 

 pointed out in Nature (vol. iii. p. 508), there is reason to 

 beliere that in these exceptional cases the males may be 



* Proc, Amer. Acad. , xii. 150. 



the selecting sex. Mr. Charles Darwin having recently 

 called my attention to a paper on this subject in Kosmos^ 

 by that most philosophical entomologist, Fritz Miiller, I 

 have thought that an abstract might interest readers of 

 Nature. 



The species of which the author treats, Epicalia 

 acontius, has such very dissimilar sexes that Fabricius 

 described them as distinct species, calling the male 

 Antiochus and the female Medea, while in Doubleday and 

 Westwood's " Genera of Diurnal Lepidoptera" the two 

 sexes are placed in different genera, the male in Epicaha 

 and the female in Myscelia. It is not known with cer- 

 tainty who first pointed out that Antiochus and Medea 

 were the sexes of the same species ; but this fact is now 



' " Epicalia acontius. Ein ungleiches Ehepaar," Kosmos, January, 1879, 

 p. 285. 



